In vehicles having internal combustion engines, it can be beneficial to discontinue fuel injection to all or some of the engine cylinders during certain operating conditions, such as during vehicle deceleration or braking. The greater the number of cylinder deactivated, or the longer cylinders are deactivated, the greater the fuel economy improvement that can be achieved.
However, the inventors herein have recognized that poor drivability may become an issue during deceleration fuel shut off (DFSO). For example, a potential exists for poor drivability when the vehicle operator releases and subsequently engages the accelerator pedal. Specifically, as described in U.S. Pat. No. 6,266,597, poor drivability may result due to transmission or driveline gear lash. In particular, when the engine transitions from exerting a positive torque to exerting a negative torque (or being driven), the gears in the transmission or driveline separate at the zero torque transition point. Then, after passing through the zero torque point, the gears again make contact to transfer torque. This series of events produces an impact, or clunk.
Further, the inventors have also recognized that the effects of transmission gear lash can be amplified depending on the state of the transmission. For example, sensitivity to noise, vibration, and harness (NVH) may be higher in all wheel drive or 4×4 operation, compared with two-wheel driver operation. Further, such sensitivity may also be increased as the overall transmission gear is lower, such as to a 4×4 low gear.
In one embodiment, drivability is improved by a method of controlling fuel injection in an engine of a vehicle having an all wheel drive or 4×4 drive system. The method comprises restricting deactivation of the fuel injection during deceleration operation when the vehicle is in an all wheel drive, or 4×4, low gear.
In another embodiment, at least some the above issues may be addressed by a method of controlling fuel injection in an engine of a vehicle having an all wheel drive system. The method comprises restricting deactivation of fuel injection during deceleration operations under conditions of an all wheel drive, or 4×4, system low gear; and disabling the fuel injection during at least some deceleration operation under other conditions.
Disabling deactivation in an all wheel drive, or 4×4, low gear allows a more controlled drivability at a time when any torque disturbance may be magnified and more easily felt by the vehicle driver. The result is improved customer satisfaction due to increased fuel economy (deactivation of fuel injection at some deceleration conditions) and off-road controllability.